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[libreriscv.git] / openpower / sv / predication.mdwn

diff --git a/openpower/sv/predication.mdwn b/openpower/sv/predication.mdwn
index 5d7a989ba64cfab3fe9b2e04a000c8b31ff14c45..31eecfafc595f26dce6107910eb047e333257ca9 100644 (file)
--- a/openpower/sv/predication.mdwn
+++ b/openpower/sv/predication.mdwn
@@ -1,6 +1,7 @@
 # TODO ideas
 
-<https://bugs.libre-soc.org/show_bug.cgi?id=213>
+<https://bugs.libre-soc.org/show_bug.cgi?id=527>
+
 
 * idea 1: modify cmp (and other CR generators?) with qualifiers that
   create single bit prefix vector into int reg
@@ -26,7 +27,7 @@
 * two modes, "zeroing" and "non-zeroing". zeroing mode places a zero in the masked-out element results, where non-zeroing leaves the destination (result) element unmodified.
 * predicate must be invertable via an opcode bit (to avoid the need for an instruction which inverts all bits of the predicate mask)
 
-Implementation note: even in in-order microarchitectures it is strongly adviseable to use byte-level write-enable lines on the register file.  This in combination with 8-bit SIMD element overrides allows, in "non-zeroing" mode, the predicate mask can very simply be directly ANDed with the regfile write-enable lines to achieve the required functionality of leaving masked-out elements unmodified.  The alternative is to perform a READ-MODIFY-MASK-WRITE cycle which is costly and compromises performance.  Avoided very simply with byte-level write-enable.
+Implementation note: even in in-order microarchitectures it is strongly adviseable to use byte-level write-enable lines on the register file.  This in combination with 8-bit SIMD element overrides allows, in "non-zeroing" mode, the predicate mask to very simply be directly ANDed with the regfile write-enable lines to achieve the required functionality of leaving masked-out elements unmodified, right down to the 8 bit element level.  The alternative is to perform a READ-MODIFY-MASK-WRITE cycle which is costly and compromises performance.  Avoided very simply with byte-level write-enable.
 
 ## General implications and considerations